1. Field of the Invention
The present invention relates to a hydraulic governor pressure supply apparatus for use with the vehicle's automatic transmissions, and more particularly to a hydraulic governor pressure supply apparatus which is adapted to be mounted to the output shaft from the automatic transmission case, and provides governor pressure output for the transmission control apparatus according to changes in the vehicle speed.
2. Description of the Prior Art
The prior art hydraulic governor pressure supply arrangement as shown in FIG. 1 includes a rotary output shaft 1 from the automatic transmission (not shown), through the interior of which shaft two parallel hydraulic fluid lines pass, one being an input passage 11 through which a hydraulic line pressure from a hydraulic fluid source flows and the other being an output passage 12 through which a regulated hydraulic governor pressure is provided. The rotary output shaft 1 has an input passage 21 and an output passage 22 therein which are connected to the respective oil passage 11 and 12 as viewed in FIG. 1. The arrangement further includes a governor valve body 2 accommodating a governor valve 23 therein which is actuated by the centrifugal force to regulate a flow through a passage connection between the input passage 21 and output passage 22, the governor valve body 2 being fitted around the rotary output shaft 1 and secured thereto by means of a clip 3. The prior art arrangement illustrated above has a problem, however, since a rising temperature in the hydraulic fluid through the arrangement causes an increasing fluid leak from the interface or jointed faces between the governor valve body 2 and rotary output shaft 1, which results in a decrease in the hydraulic governor pressure. The causes for this problem may be summarized as follows.
(1) The rotary shaft 1 is usually made of steel iron while the governor valve body 2 is made of alluminum alloy. Those different materials used have a different thermal expansion coefficient, which causes a gap to be produced between the jointed faces of the two components;
(2) A rise in the fluid temperature decreases the viscosity of the fluid; and
(3) The line pressure and governor pressure being exerted upon the governor valve body 2 in the region A of the jointed faces adjacent to the respective connecting points between the input passages and output passages in the interface between the rotary shaft 1 and governor valve body 2 cause the governor valve body 2 to deviated from the axial center of the rotary shaft 1 to the extent that a greater gap is produced near the points at which the input and output passages are interconnected, respectively. Such loss in the governor pressure may possibly cause the automatic shifting to fail or operate improperly during the vehicle running conditions. The improperly operated shifter may possibly provide an unexpected downshifting from the fourth speed to third speed when the vehicle is running at the highest fourth speed, causing the engine brake to work unexpectedly, the engine to overrun and/or the wheels to spin. In practically all automatic transmissions recently developped and actually installed in vehicles, the automatic shifting point setting usually takes place at the high speed. However, the prior art hydraulic governor pressure supply apparatus used in those vehicles causes a greater amount of hydraulic fluid leak therefrom to occur as clearly shown by the characteristic curve I in FIG. 2, as the vehicle reaches a speed above a certain speed (such as 120 km/h in FIG. 2). This leak decreases the governor pressure, making the automatic shifting in the high speed range difficult or almost impossible.